1. Technical Field
The present invention relates to a droplet discharging device and a method for heating a functional liquid of a droplet discharging device.
2. Related Art
Ink-jet devices that discharge a functional liquid in droplets, namely droplet discharging devices have drawn attention as a device for forming a desired pattern on a substrate. The droplet discharging devices move a substrate placed on a stage thereof two-dimensionally relative to a droplet discharge head that discharges the functional liquid in droplets so as to dispose the droplets discharged from the droplet discharge head on predetermined positions of a surface of the substrate, forming a pattern.
In the droplet discharging devices, if the viscosity of the functional liquid is unstable, the droplet weight changes, causing variation of the pattern in size or in shape. Further, when the viscosity of the functional liquid is high, a nozzle of the droplet discharge head is clogged, causing a droplet-discharging defect. Therefore, the droplet discharging devices cool the functional liquid that is to be supplied to the droplet discharge head by a cooling means or heat it by a heating means so as to control the viscosity of the functional liquid, as disclosed in JP-A-2000-238281 and JP-A-2005-305973, for example.
A method for forming a wiring pattern on a substrate irradiates the droplet with a laser beam for high accuracy of wiring width, that is, high accuracy of a diameter of the droplet. The discharged droplet is irradiated with the laser beam to be dried in a short time, being able to prevent the droplet from spreading after it lands. As the functional liquid for forming such wiring pattern, a dispersion-based metal ink obtained by dispersing metal particulates of silver (Ag), for example, in a solvent is known.
When the metal ink mentioned above is left at a room temperature, a secondary aggregation or the like occurs in the ink, deteriorating the ink. In a case where the droplet discharging devices are driven continuously for a long time, the metal ink stored in a tank is kept to be at the room temperature to deteriorate. Thus a stable operation is difficult. Therefore, in a case where the metal ink is used, it is necessary that the tank is cooled by the cooling means so as to cool the ink.
On the other hand, if the metal ink that is stored in the tank is cooled down, the metal ink at a low temperature is supplied from the tank to the droplet discharge head. As a result, it is difficult for the droplet discharge head to discharge the ink in droplets because the metal ink is at a low temperature, that is, has high viscosity. This problem can be solved such that the heating means is provided to a supply tube that couples the tank and the droplet discharge head so as to heat the metal ink flowing in the supply tube. Thus the metal ink that is not used is cooled by the cooling means so as to be prevented from deteriorating and the metal ink that is in use is heated by the heating means so as to decrease the viscosity thereof.
However, the above structure includes the heating means and the cooling means separately, increasing power consumption and causing a larger size of the droplet discharging device.